In order to provide complete suppression of voltage transients in electrical circuits, and particularly circuits that include hot, neutral, and ground conductors, it is desirable to provide surge suppressors, such as metal oxide varistors, bridging each of the three possible pairs of conductors in which these voltage transients can occur. More specifically, it is desirable to provide a surge protection device connected between the hot and neutral lines, between the hot and ground lines, and between the neutral and ground lines.
Some forms of transient voltage surge suppression devices, such as varistors, are subject to failure during operation, either as a result of high energy transient voltages being applied to the devices, the repetitive application of lower energy transient voltages, or even the long term application of steady state voltages above the suppression threshold. Any one of these may lead to immediate failure.
The failure mode associated with metal oxide varistors, produces a short circuit or low impedance failure. That is, the impedance of the device is reduced significantly below its normal operating impedance, as a result of failure. It is known to protect electrical circuits against such failure, by providing fuses in series with the varistors so that if the varistors fail, the fuses open and the varistor does not itself cause a short circuit or low impedance condition on the power circuit, which could create a risk of overloading the circuit, leading to overheating, the tripping of remote circuit breakers, or the like.
When a metal oxide varistor fails in a way that causes a series connected fuse to open, the protection provided by the varistor is lost. Moreover, the failure may be undetectable by observation of the device or devices connected to the circuit. Therefore it is possible for the transient voltage protection to be lost without any obvious signs thereof, and thereafter for voltage transients to be passed unsuppressed to the equipment connected to the previously protected circuit, possibly causing damage.
In an effort to provide some indication of the failure of certain suppression devices, particularly varistors, indicators have been provided. Such indicators may be visual, such as a light emitting diode or other visible device; or audible such as a buzzer, horn or the like. While such devices are effective in indicating the loss of surge suppression, the additional components required to provide such indicators are expensive, increase the overall cost of the transient voltage surge suppression device, and therefore to some extent reduce the number of applications in which the surge suppression devices may be used. Suppression devices with indicators have been provided that overcome this problem to some extent by providing inexpensive indicator devices, either a light and/or an audible device, that indicates the failure of one or two legs of the surge suppressor, but to date, no device is known that uses a single indicator for indicating a failure of any one of three surge suppressors connected between the previously described pairs of lines in a two-wire plus ground electrical circuit.
While audible failure indicators are particularly desirable in applications where the surge suppression device is mounted in a visually inaccessible area, an audible alarm can itself cause problems. In applications where a fault occurs and an audible alarm sounds, it may be some time before a repair can be effected. Since surge suppression devices are often combined with electrical receptacles which are permanently connected to electrical circuits, trained personnel are needed to effect a replacement in the event of a fault.
In residential settings, or even in commercial or industrial settings, a trained person is not always immediately available. In these cases, the incessant buzzing of an audible alarm may be distressing to residents forced to listen to it during the time it takes for the device to be replaced. To this end, it is known to provide an audible alarm that can be deactivated, for example, by turning a screw that engages the diaphragm of a buzzer, thereby quieting it, or breaking a circuit trace connecting the buzzer to its power source, each of which effectively quiets the buzzer, but may do so in an irreversible fashion. Since the control for deactivating the buzzer must be accessible on the outside of the device, it may happen that the control is either accidentally or even maliciously engaged before a fault occurs, thereby in some instances rendering the audible portion of the alarm ineffective in the event of a failure. It would be advantageous to provide a control for disengaging an audible alarm that can be switched from an engaged position to a disengaged position repeatedly, so that if the alarm is accidentally disengaged before a fault occurs, the device is not thereby rendered inoperative in the future. It is desirable to do this switching electrically rather than mechanically, so as to provide repeatable engagement and disengagement without damage as may occur with a mechanical approach. Moreover, it is desirable to provide a control for disengaging an audible alarm that can be operated with readily available tools, such as the pointed tip of a pencil or pen, or the like, rather than requiring a screw driver or other tool that may not be available when needed. Such a device has the additional advantage of preventing accidental disengagement of the audible alarm.
It is an object of this invention to provide a transient voltage surge suppressor (TVSS) that overcomes the problems mentioned before.
It is a more particular object of this invention to provide an electrical receptacle with integral transient voltage suppression that includes an indicator light that is responsive to the failure of any of three transient voltage surge suppression devices, particularly metal oxide varistors, to provide a visible indication of such failure, so that the device can be replaced.
It is another object of this invention to provide an electrical receptacle that includes integral transient voltage surge suppression, together with an audible alarm that includes an actuator for selectively engaging or disengaging the alarm.
It is an even more particular object of the invention to provide a TVSS with such an actuator that can be repeatedly turned on or off without destroying or otherwise impairing the functioning of the audible alarm.
It is an even more specific object of the invention to provide a TVSS with an actuator for the alarm that can be disengaged with a simple tool, such as a pointed pen or pencil.